mj-group allows you to prevent columns from stacking on mobile. To do so, wrap the columns inside a mj-group tag, so they'll stay side by side on mobile.
Column inside a group must have a width in percentage, not in pixel.
You can have both column and group inside a Section.
You can use the following attribute -
width represents the width of the group.
<mjml>
<mj-body>
<mj-section>
<mj-group>
<mj-column>
<mj-image width="137px" height="185px" padding="0" src="https://mjml.io/assets/img/easy-and-quick.png" />
<mj-text align="center">
<h2>Easy and quick</h2>
<p>Write less code, save time and code more efficiently with MJML’s semantic syntax.</p>
</mj-text>
</mj-column>
<mj-column>
<mj-image width="166px" height="185px" padding="0" src="https://mjml.io/assets/img/responsive.png" />
<mj-text align="center">
<h2>Responsive</h2>
<p>MJML is responsive by design on most-popular email clients, even Outlook.</p>
</mj-text>
</mj-column>
</mj-group>
</mj-section>
</mj-body>
</mjml>